Method of producing display device, display device, method of producing thin-film transistor substrate, and thin-film transistor substrate

ABSTRACT

A method of producing a display device includes the steps of forming gate electrodes on a substrate so that an arrangement of a source and a drain, in a pixel row direction, of a thin-film transistor formed in each of pixels on the substrate is reversed every pixel row; forming a gate insulating film and an amorphous semiconductor thin film on the substrate in that order so as to cover the gate electrodes; crystallizing the semiconductor thin film by irradiating the semiconductor thin film with an energy beam so that a scanning direction of the energy beam is the same with respect to the arrangement of the source and the drain in the pixel row direction; and forming a light-emitting element connected to the thin-film transistor.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.12/379,337, filed Feb. 19, 2009, which claims priority from JapaneseApplication Nos.: 2008-077400, filed on Mar. 25, 2008 and JapaneseApplication No.: 2008-323361, filed on Dec. 19, 2008, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a display device,a display device, a method of producing a thin-film transistorsubstrate, and a thin-film transistor substrate. In particular, thepresent invention relates to a method of producing an activematrix-driving display device including organic electroluminescentelements, the structure thereof, a method of producing a thin-filmtransistor substrate that is suitably used in the display device, and athin-film transistor substrate.

2. Description of the Related Art

In an active matrix-driving display device in which organicelectroluminescent elements and pixel circuits connected thereto arearranged on a substrate, the luminance of each of the organicelectroluminescent elements is determined by the amount of current of athin-film transistor (TFT) constituting the pixel circuit. Therefore, inorder to obtain a display device in which uneven luminance is suppressedand which has satisfactory display properties, it is important thatvariation in properties of the thin-film transistor be suppressed.

In the case where a channel region of a thin-film transistor is formedof polycrystalline silicon, the size of crystal grains present in thechannel region is nonuniform, and thus transistor characteristicsreadily vary. Consequently, as a method of microcrystallizing asemiconductor thin film constituting the channel region to the extentthat the size of the crystal grains is not nonuniform, crystallizationannealing, in which an amorphous thin film is microcrystallized using asolid-state laser, has been performed.

FIG. 23 shows an arrangement on a thin-film transistor substrate forillustrating a step of the above-mentioned crystallization annealing.FIG. 24 shows the arrangement of two display pixels in the thin-filmtransistor substrate. As shown in these figures, in a process ofproducing a medium or small size display panel, for example, two displaypanels 2 are arranged on a single glass substrate 1. In this case, ashort side of each of the display panels 2 is arranged so as to beparallel to a long side of the glass substrate 1. In each of the displaypanels 2, a display area 2 a having a shape that is substantiallysimilar to the shape of the display panel 2 is defined. In each of thedisplay areas 2 a, sub-pixels a each having a rectangular shape in planview are arranged. The sub-pixels a are arranged such that a long sideof each of the sub-pixels a is parallel to a short-side direction y ofthe display area 2 a. Furthermore, these sub-pixels a constitutesubstantially square display pixels A each composed of a set of threesub-pixels a of red (R), green (G), and blue (B), the three sub-pixels abeing arranged in a direction of a short side of each of the sub-pixelsa.

In the display area 2 a in each of the display panels 2, scanning lines11 and power lines 12 are arranged in a long-side direction x of thedisplay area 2 a, and signal lines 13 are arranged so as to beperpendicular to the scanning lines 11 and the power lines 12. Thesub-pixels a are arranged so as to correspond to intersecting portionsof these lines. In each of the sub-pixels a, thin-film transistors Tr1′and Tr2′ each including a gate electrode 14 extending parallel to thesignal lines 13, and a capacitive element Cs are arranged. In this case,by reversely disposing an arrangement of adjacent sub-pixels a, a partof the power line 12 can be shared, and thus a distance between wiringsin a display pixel can be increased. As a result, short-circuit causedby, for example, a mixing of dust in a production process and generationof defects of the display pixel can be suppressed to improve the yield.In particular, a pixel circuit for diving an organic electroluminescentelement includes a large number of elements, and thus it is important toincrease the distance between wirings.

In order to make the above-described thin-film transistor substrate, thestep of crystallization annealing is performed as follows. First, asshown in FIG. 25, gate electrodes 14 composed of a first metal pattern21 are formed in each of display areas 2 a on a glass substrate 1, andother wiring portions composed of the first metal pattern 21, such asparts of signal lines 13 and lower electrodes of capacitive elements Cs,are also formed at the same time. Next, a gate insulating film 31 and anamorphous semiconductor thin film 32 are formed in that order so as tocover the first metal pattern 21. Furthermore, a buffer layer and aphotothermal conversion layer (not shown) are optionally formed thereon.Next, the semiconductor thin film 32 is irradiated with a laser beamthrough these layers while scanning the laser beam. Thereby, asemiconductor thin film 32 portion corresponding to a portion irradiatedwith the laser beam is microcrystallized to form a semiconductor thinfilm 32A.

In this case, a scanning direction v (−v) of the laser beam is parallelto the long-side direction x of the display area 2 a. That is, as shownin FIG. 23, the scanning direction v (−v) of the laser beam is parallelto a short side of the substrate 1. Accordingly, variation in energy ofa laser beam Lh due to a long scanning distance of the laser beam can beprevented, thereby forming more uniform crystals. In this case, in theexample shown in FIG. 24, a channel length direction of each of thethin-film transistors Tr1′ and Tr2′ corresponds to the scanningdirection v (−v) of the laser beam.

After the above-described step of crystallization annealing, as shown inthe plan view of FIG. 26A and the cross-sectional view of FIG. 26B, thesemiconductor thin film 32A, which has been microcrystallized, ispatterned so as to have a shape covering the gate electrode 14.Furthermore, an etching stopper layer 33 is formed so as to overlap withthe gate electrode 14. Note that FIG. 26B is a cross-sectional viewtaken along line XXVIB-XXVIB in FIG. 26A. Next, a source/drain 34 sd(shown in only the cross-sectional view) composed of an n-typesemiconductor thin film is formed so that the source/drain 34 sdoverlaps with the semiconductor thin film 32A and is separately disposedon the etching stopper layer 33. Subsequently, a source electrode/drainelectrode 22 sd composed of a second metal pattern 22 is further formed,thus obtaining the thin-film transistors Tr1′ and Tr2′. Other wiringportions composed of the second metal pattern 22, for example, thescanning lines 11, the power lines 12, and upper electrodes of thecapacitive elements Cs, all of which are shown in FIG. 24, are alsoformed together with the source electrode/drain electrode 22 sd.

In the above-mentioned crystallization annealing using a solid-statelaser, a thermal diffusion length when a heat quantity necessary forcrystallizing a semiconductor thin film is supplied is longer than thatin the case of crystallization annealing using an excimer laser.Accordingly, an effect of heat conduction by the gate electrode 14,which is provided under the semiconductor thin film 32, is significant,and thus crystallinity of the semiconductor thin film 32 is affected.

Consequently, the following structure has been proposed. As shown inFIG. 26, the gate electrode 14 of the thin-film transistors Tr1′ andTr2′ is provided so as to extend in the channel length direction (i.e.,the dimension of the gate electrode 14 is increased in a widthdirection), and the extending portions ALs and ALd are used as heattransfer components. According to this structure, in the step ofcrystallization annealing described above, the effect of heat conductionby the gate electrode 14 is made to be uniform in a channel regionoverlapping with the gate electrode 14. Consequently, uniformcrystallinity of the channel region can be realized (see JapaneseUnexamined Patent Application Publication No. 2007-35964).

SUMMARY OF THE INVENTION

Even when the dimension of the gate electrode 14 disposed under thesemiconductor thin film 32 is increased in the line width direction asdescribed with reference to FIG. 26, the crystallinity of thesemiconductor thin film above the gate electrode 14 is varied dependingon a scanning direction of a laser beam. More specifically, in the casewhere the line width direction (i.e., channel length direction) of thegate electrode 14 is the scanning direction of the laser beam, the gateelectrode 14 is not readily thermally saturated at the upstream side ofthe scanning direction, whereas the gate electrode 14 is readilythermally saturated at the downstream side of the scanning direction.

Therefore, at the upstream side of the scanning direction v (−v) of thelaser beam with respect to the gate electrode 14, crystallization of thesemiconductor thin film 32 tends to be performed before the gateelectrode 14 is sufficiently heated by the irradiation of the laserbeam. Consequently, crystallinity at the upstream side is low. Incontrast, at the downstream side of the scanning direction v (−v) of thelaser beam with respect to the gate electrode 14, crystallization of thesemiconductor thin film 32 is performed after the gate electrode 14 issufficiently heated by the irradiation of the laser beam. Consequently,crystallinity at the downstream side is high.

Accordingly, in the thin-film transistors Tr1′ and Tr2′ arranged asshown in FIG. 24, a portion having low crystallinity and a portionhaving high crystallinity are formed at ends in a channel lengthdirection in the channel region of the semiconductor thin film. Suchvariation in crystallinity in the channel length direction in thechannel region significantly affects an on-current of the thin-filmtransistors. Table 1 shows values of an on-current of thin-filmtransistors formed positions 1 to 12 (see FIG. 27) in the case where thescanning direction v (v) of the laser beam during crystallizationannealing is changed. In one case, the source side of each of thethin-film transistors Tr1′ and Tr2′ is upstream of the scanningdirection. In another case, the drain side thereof is upstream of thescanning direction. As shown in FIG. 27, the values of the on-currentare values for the thin-film transistors formed at positions 1 to 12separately disposed on a display panel 2 of a substrate. The ratio W/Lof a gate width W to a gate length L of each of the thin-filmtransistors is 20/8.

TABLE 1 Scanning direction of laser beam Upstream: Upstream: source sidedrain side Position On-current value 1 2.35E−06 2.61E−06 2 2.33E−062.59E−06 3 1.98E−06 2.17E−06 4 1.87E−06 2.03E−06 5 2.48E−06 2.70E−06 62.51E−06 2.71E−06 7 2.20E−06 2.40E−06 8 2.06E−06 2.23E−06 9 2.59E−062.77E−06 10 2.63E−06 2.66E−06 11 2.40E−06 2.47E−06 12 1.94E−06 2.08E−06Vg = 10 V, Vd = 10 V

As is apparent from Table 1, when a side at which crystallinity is low(i.e., the upstream side of the scanning direction) is a drain, theon-current is large. In contrast, when the side at which crystallinityis low (i.e., the upstream side of the scanning direction) is a source,the on-current is small.

Accordingly, in the case where adjacent sub-pixels a are reverselyarranged as shown in FIG. 24, the arrangements of the thin-filmtransistors Tr1′ and Tr2′ of sub-pixels a for the same color in adjacentdisplay pixels are reversed. Therefore, in the thin-film transistorsTr1′ and Tr2′ of the sub-pixels a for the same color, a transistorcharacteristic, e.g., the on-current, is varied because of theabove-described variation in crystallinity at ends in the channel lengthdirection. Accordingly, in the sub-pixels a for the same color in theadjacent display pixels, a difference in the luminance betweenlight-emitting elements each connected to the thin-film transistors Tr1′and Tr2′ is generated. As a result, the difference in the luminancebetween the adjacent display pixels is visually recognized as unevenluminance.

Alternatively, for example, in order to reduce the time necessary forthe step of crystallization annealing, laser irradiation is performed ina scanning direction v for a first sub-pixel a row, and laserirradiation is then performed in a scanning direction −v for a secondsub-pixel a row. That is, in a reciprocating scanning of a laser beam,laser irradiation is performed for sub-pixels a arranged in differentrows. In such a case, a difference in a characteristic of thin-filmtransistors is generated every row, resulting in a difference in theluminance between light-emitting elements connected to the thin-filmtransistors.

It is desirable to provide a method of producing a display device havinggood display properties, by which thin-film transistors in whichon-currents are uniform can be obtained, and thus uneven luminance oflight-emitting elements connected to the thin-film transistors can beprevented, while decreasing the time necessary for a step ofcrystallization annealing of a semiconductor thin film. Furthermore, itis desirable to provide a display device produced by the method.

A method of producing a display device and a method of producing athin-film transistor substrate according to an embodiment of the presentinvention include the following steps. First, gate electrodes are formedon a substrate so that an arrangement of a source and a drain, in apixel row direction, of a thin-film transistor formed in each of pixelson the substrate is reversed every pixel row. Next, a gate insulatingfilm and an amorphous semiconductor thin film are formed on thesubstrate in that order so as to cover the gate electrodes.Subsequently, the semiconductor thin film is crystallized by irradiatingthe semiconductor thin film disposed above the gate electrodes with anenergy beam so that a scanning direction of the energy beam is the samewith respect to the arrangement of the source and the drain in the pixelrow direction while scanning the energy beam. In producing the displaydevice, a light-emitting element connected to the thin-film transistorthus formed is further formed.

Embodiments of the present invention also provide a display device inwhich thin-film transistors obtained by the above production method areconnected to light-emitting elements, and a thin-film transistorsubstrate. The display device according to an embodiment of the presentinvention includes first pixel rows each including thin-film transistorseach having a source and a drain arranged in a first direction, secondpixel rows each including thin-film transistors each having a source anda drain arranged in a second direction opposite to the first direction,and a plurality of light-emitting elements connected to the thin-filmtransistors.

In the method according to an embodiment of the present invention, incrystallization of the semiconductor thin film by irradiation of anenergy beam, the energy beam is scanned so that a scanning direction isthe same with respect to the arrangement of the source and the drain inthe pixel row direction. Accordingly, portions of the semiconductor thinfilm disposed above the gate electrodes are constantly scanned by theenergy beam in a direction from a drain side to a source side (or in thereverse direction). Therefore, a difference in crystallinity between aportion of the semiconductor thin film at the source side and a portionof the semiconductor thin film at the drain side, the difference beingcaused by a difference in the scanning direction of the energy beam withrespect to the gate electrodes, is constant in the thin-filmtransistors. In addition, the gate electrodes are formed so that thearrangement of the source and the drain in the pixel row direction isreversed every pixel row. Therefore, in order to scan the energy beam sothat the scanning direction is the same with respect to the arrangementof the source and the drain in the pixel row direction as describedabove, both the plus direction and the minus direction of the pixel rowdirection are necessary as the scanning direction. Accordingly, scanningof the energy beam is performed in the pixel row direction in areciprocating manner.

As described above, according to an embodiment of the present invention,by performing a reciprocating scanning of an energy beam in the pixelrow direction, the time necessary for the step of crystallizationannealing of the semiconductor thin film can be reduced. In addition, adifference in crystallinity between a portion of the semiconductor thinfilm at the source side and a portion of the semiconductor thin film atthe drain side, the difference being caused by a difference in thescanning direction of the energy beam, is constant in the thin-filmtransistors. Consequently, thin-film transistors in which the on-currentis uniform can be produced. As a result, a display device which hassatisfactory display properties and in which uneven luminance oflight-emitting elements connected to thin-film transistors is preventedcan be produced within a further reduced turn-around time (TAT).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an arrangement on a substrate illustrating afirst embodiment;

FIG. 2 is a view showing an arrangement of six pixels (sub-pixels)illustrating the first embodiment;

FIG. 3 is a circuit diagram of each of the sub-pixels;

FIG. 4 is a plan view of the six pixels (sub-pixels) illustrating a stepin a production process of the first embodiment;

FIGS. 5A to 5D are cross-sectional views (part 1) illustrating theproduction process of the first embodiment;

FIGS. 6A to 6D are cross-sectional views (part 2) illustrating theproduction process of the first embodiment;

FIG. 7 is a cross-sectional view illustrating a process of producing alight-emitting element of the first embodiment;

FIG. 8 is an overall view of a display device of the first embodiment;

FIG. 9 is a view showing an arrangement of six pixels (sub-pixels)illustrating a feature of a second embodiment;

FIG. 10 is a plan view of the six pixels (sub-pixels) illustrating astep in a production process of the second embodiment;

FIG. 11 is a view showing an arrangement of six pixels (sub-pixels)illustrating a feature of a third embodiment;

FIG. 12 is a plan view of the six pixels (sub-pixels) illustrating astep in a production process of the third embodiment;

FIG. 13 is a graph showing current characteristics of thin-filmtransistors prepared by changing a scanning direction of a laser beamduring crystallization annealing;

FIG. 14 is a graph showing the relationship between a signal-writingtime and a current value of thin-film transistors prepared by changing ascanning direction of a laser beam during crystallization annealing;

FIG. 15 is a view showing an arrangement on a substrate illustrating afourth embodiment;

FIG. 16 is a plan view of six pixels (sub-pixels) illustrating a step ina production process of a fifth embodiment;

FIG. 17 is a plan view of the six pixels (sub-pixels) illustrating astep in the production process of the fifth embodiment;

FIG. 18 is a perspective view showing a television to which anembodiment of the present invention is applied;

FIGS. 19A and 19B are perspective views showing a digital camera towhich an embodiment of the present invention is applied;

FIG. 20 is a perspective view showing a notebook personal computer towhich an embodiment of the present invention is applied;

FIG. 21 is a perspective view showing a video camera to which anembodiment of the present invention is applied;

FIGS. 22A to 22G are views showing a mobile terminal device, e.g., amobile phone, to which an embodiment of the present invention isapplied;

FIG. 23 is a view showing an arrangement on a thin-film transistorsubstrate illustrating a step of crystallization annealing in producinga display device in the related art;

FIG. 24 is a view showing an arrangement of two display pixelsillustrating the step of crystallization annealing in producing thedisplay device in the related art;

FIG. 25 is a plan view of the two display pixels illustrating a step ina process of producing the display device in the related art;

FIGS. 26A and 26B are views illustrating the process of producing thedisplay device in the related art; and

FIG. 27 includes views illustrating positions on a substrate used formeasuring values of an on-current and scanning directions of a laserbeam for thin-film transistors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments in which the present invention is applied to an activematrix display device including thin-film transistors and organicelectroluminescent elements connected to the thin-film transistors willnow be described in detail with reference to the drawings. Theembodiments will be described in the following order.

-   1. First embodiment (An example in which a source/drain arrangement    of a thin-film transistor for driving is reversed every pixel row    and two pixel rows share a power line)-   2. Second embodiment (An example in which a source/drain arrangement    of a thin-film transistor for driving is reversed every pixel row)-   3. Third first embodiment (An example in which a source/drain    arrangement of each of a thin-film transistor for driving and a    thin-film transistor for switching is reversed every pixel row and    two pixel rows share a power line)-   4. Fourth embodiment (An example in which pixel rows in which a    source/drain arrangement is reversed are separately arranged in two    areas in a display area)-   5. Fifth embodiment (An example in which pixel circuits of only blue    sub-pixels among sub-pixels arranged in a pixel row direction are    reversed)

In each of the embodiments, a procedure of producing an active matrixdisplay device wherein light-emitting elements are connected tothin-film transistors will be sequentially described from a process ofproducing a thin-film transistor substrate. In the description, the samecomponents as those in the structure in the related art described withreference to FIGS. 23 to 26 are assigned the same reference numerals andsymbols.

First Embodiment

An arrangement on a thin-film transistor substrate for carrying out aproduction method of a first embodiment will now be described withreference to FIGS. 1 and 2. For reference, a circuit diagram of eachsub-pixel is shown in FIG. 3.

As shown in FIG. 1, a glass substrate 1 having a rectangular shape inplan view is prepared. Next, areas for forming, for example, two displaypanels 2 are defined on the glass substrate 1. In this step, a shortside of each of the display panels 2 is arranged so as to parallel to along side of the glass substrate 1 so that the two display panels 2 canbe efficiently arranged on the single glass substrate 1. In each of thedisplay panels 2, a display area 2 a having a rectangular shape in planview that is substantially similar to the shape of the display panel 2is defined. In each of the display areas 2 a, sub-pixels a each having arectangular shape in plan view are arranged. These sub-pixels a arearranged such that a long-side of each of the sub-pixels a is parallelto a short-side direction y of the display area 2 a. Furthermore, thesesub-pixels a constitute substantially square display pixels eachcomposed of a set of three sub-pixels, namely, a red (R) sub-pixel a(R),a green (G) sub-pixel a(G), and a blue (B) sub-pixel a(B), the threesub-pixels a being arranged in a direction of a short side of each ofthe sub-pixels a. This arrangement is the same as that in the relatedart.

As shown in FIG. 2, in each of the display areas 2 a, scanning lines 11and power lines 12 are arranged in a long-side direction x of thedisplay area 2 a, and signal lines 13 are arranged so as to beperpendicular to the scanning lines 11 and the power lines 12. In thisembodiment, in particular, a power line 12 is disposed between twoscanning lines 11. The sub-pixels a are arranged so as to correspond tointersecting portions of these scanning lines 11 and power lines 12, andthe signal lines 13.

In each of the sub-pixels a, a thin-film transistor for switching(hereinafter referred to as a “switching transistor”) Tr1 and athin-film transistor for driving (hereinafter referred to as a “drivingtransistor”) Tr2, and a capacitive element Cs are arranged (see FIG. 3),and these transistors and the capacitive element Cs constitute apixel-driving circuit. In the switching transistor Tr1, a gate electrodeis connected to a scanning line 11, a drain D is connected to a signalline 13, and a source S is connected to the capacitive element Cs andthe driving transistor Tr2. In the driving transistor Tr2, a gateelectrode is connected to the capacitive element Cs and the switchingtransistor Tr1, a drain D is connected to a power line 12, and a sourceS is connected to an electroluminescent element EL.

In each pixel-driving circuit having the above structure, a picturesignal written from the signal line 13 through the switching transistorTr1 selected in the scanning line 11 is held in the storage capacitorCs. A current corresponding to the amount of held signal is suppliedfrom the source S of the driving transistor Tr2 to theelectroluminescent element EL. The electroluminescent element EL emitslight with a luminance corresponding to the value of this current.

Each of electroluminescent elements EL provided in sub-pixels a(R),a(G), and a(B) emits light with a luminance corresponding to the currentvalue of the corresponding driving transistor Tr2. Therefore, thedriving transistors Tr2 provided in the sub-pixels a(R), a(G), and a(B)have channel widths that are different depending on the luminousefficiency of the electroluminescent elements EL for each color providedin the sub-pixels. More specifically, in a sub-pixel including anelectroluminescent element EL for a color with a low luminousefficiency, the channel width of the driving transistor Tr2 isdetermined to be large. Here, for example, it is assumed that theluminous efficiency of a blue electroluminescent element EL is thelowest and the channel width of the driving transistor Tr2 in the bluesub-pixel a(B) is the largest, the channel width of the drivingtransistor Tr2 in the green sub-pixel a(G) is the second largest, andthe channel width of the driving transistor Tr2 in the red sub-pixela(R) is the smallest.

In each of the sub-pixels a, the thin-film transistors Tr1 and Tr2 arearranged as bottom-gate thin-film transistors. These thin-filmtransistors Tr1 and Tr2 are arranged so that a channel length directionthereof is parallel to a short side of the sub-pixel a, that is, gateelectrodes 14 a and 14 b extend in a long-side direction of thesub-pixel a, i.e., in the short-side direction y of the display area 2a.

Furthermore, in particular, when a row of sub-pixels a parallel to ascanning line 11 is defined as a pixel row, in each of the display areas2 a, first pixel rows Al and second pixel rows A2 are arranged inaccordance with a source S/drain D arrangement of the driving transistorTr2. In the first pixel rows A1 and the second pixel rows A2, the sourceS and the drain D of the driving transistor Tr2 are reversely arrangedwith respect to the direction of the pixel rows. More specifically, ineach of sub-pixels a in the first pixel rows A1, the drain D and thesource S of the driving transistor Tr2 are arranged in that order in afirst direction (for example, in a direction from the left to the rightin FIG. 2). In contrast, in each of sub-pixels a in the second pixelrows A2, the drain D and the source S of the driving transistor Tr2 arearranged in that order in a second direction opposite to the firstdirection (for example, in a direction from the right to the left inFIG. 2).

Preferably, the first pixel rows A1 and the second pixel rows A2 arealternately arranged so as to be adjacent to each other along theextending direction of the signal lines 13. The driving transistors Tr2arranged in a first pixel row A1 and the driving transistors Tr2arranged in a second pixel row A2, the first pixel row A1 and the secondpixel row A2 being alternately arranged, share a power line 12.

A thin-film transistor substrate having the above-described arrangementis prepared by the following procedure.

First, as shown in the plan view of FIG. 4 and the cross-sectional viewof FIG. 5A (corresponding to a cross-sectional view taken along lineVII-VII in the plan view of FIG. 2), gate electrodes 14 a and 14 bcomposed of a first metal pattern 21 are formed on each of display areas2 a of a glass substrate 1, and furthermore, other wiring portionscomposed of the first metal pattern 21, for example, parts of signallines 13 and lower electrodes of capacitive elements Cs, are alsoformed. In this step, the gate electrodes 14 a of switching transistorsTr1 and the gate electrodes 14 b of driving transistors Tr2 arepatterned so as to extend in a direction parallel to a short-sidedirection y of the display area 2 a. The parts of the signal lines 13are patterned so as to extend in the direction parallel to theshort-side direction y of the display area 2 a.

In particular, the gate electrodes 14 b of the driving transistors Tr2are provided such that a source S/drain D arrangement in an arrangementdirection of sub-pixels a is reversed every pixel row extending in adirection perpendicular to an extending direction of the signal lines13. More specifically, in each of the display areas 2 a, first pixelrows A1 and second pixel rows A2 are arranged in accordance with thesource S/drain D arrangement of the driving transistors Tr2. In thefirst pixel rows A1 and the second pixel rows A2, the source S/drain Darrangement of the driving transistors Tr2 is reversed in thearrangement direction of the sub-pixels a. The gate electrode 14 b ofthe driving transistor Tr2 is formed as a pattern that is continuouswith the lower electrode of the capacitive element Cs. A portionconstituting the gate electrode 14 b in this continuous pattern isprovided so as to extend in a direction parallel to the short-sidedirection y of the display area 2 a.

The first metal pattern 21 including the gate electrodes 14 a and 14 bis formed by, for example, depositing a molybdenum (Mo) film by asputtering method, and then pattern-etching the molybdenum (Mo) filmusing a resist pattern as a mask. The material of the first metalpattern 21 is not limited to molybdenum (Mo) as long as the material isa refractory metal that is not readily degraded in a subsequent heatingstep.

Next, a gate insulating film 31 made of, for example, silicon oxide orsilicon nitride is deposited so as to cover the first metal pattern 21,and a semiconductor thin film 32 made of amorphous silicon issubsequently deposited on the gate insulating film 31.

Subsequently, as shown in FIG. 5B, a buffer layer 41 made of siliconoxide or silicon nitride is deposited so as to cover the semiconductorthin film 32. Subsequently, a photothermal conversion layer 42 made ofmolybdenum (Mo) is deposited on the buffer layer 41. This photothermalconversion layer 42 is a layer for absorbing an energy beam such as alaser beam described below and converting light energy to heat energy.Accordingly, any material may be used as the photothermal conversionlayer 42 as long as the material satisfies the conditions that, forexample, the absorption rate of a laser beam (energy beam) used incrystallization annealing in the subsequent step is high, thermaldiffusion rates to the buffer layer 41 and the semiconductor thin film32 are low, and the material has a high melting point so as not to bereadily degraded by heat generated in the subsequent crystallization.Alternatively, for example, carbon (C) may be used.

Subsequently, as shown in FIG. 5C and the plan view of FIG. 4, thesemiconductor thin film 32 is indirectly irradiated with a laser beam Lhthrough the photothermal conversion layer 42 and the buffer layer 41,thus performing a heat treatment on the semiconductor thin film 32. Inthis step, a laser beam emitted from an oscillation source composed of asolid-state laser is irradiated as the laser beam Lh. Consequently, aportion of the semiconductor thin film 32, the portion being irradiatedwith the laser beam Lh, is formed into a microcrystalline silicon thinfilm 32A (semiconductor thin film 32A) crystallized so as to havecrystal grains on the nanometer order.

In the irradiation of the laser beam Lh in this step, it is importantthat the semiconductor thin film 32 disposed above the gate electrode 14b be irradiated with the laser beam Lh while scanning the laser beam Lhsuch that a scanning direction of the laser beam Lh is the same withrespect to the arrangement of the source S and the drain D in adirection of a row of the sub-pixels a (i.e., here, in a directionperpendicular to the signal lines 13).

For this purpose, in this step, the scanning direction v (−v) of thelaser beam Lh with respect to the arrangement direction of thesub-pixels a is reversed between the first pixel rows A1 and the secondpixel rows A2. Specifically, for the first pixel rows A1, thesemiconductor thin film 32 is irradiated with the laser beam Lh in ascanning direction v (−v) of the laser beam Lh. In contrast, for thesecond pixel rows A2, the semiconductor thin film 32 is irradiated withthe laser beam Lh in a scanning direction −v (v) of the laser beam Lh.In particular, the scanning direction v (−v) of the laser beam Lh ispreferably determined so that the source S side of the drivingtransistor Tr2 is downstream and the drain D side thereof is upstream.Accordingly, the semiconductor thin film 32 is preferably irradiatedwith the laser beam Lh in the scanning direction v for the first pixelrows A1 and in the scanning direction −v for the second pixel rows A2.Consequently, each of the display area 2 a can be irradiated with thelaser beam Lh while scanning the laser beam Lh in the long-sidedirection x of the display area 2 a in a reciprocating manner.

In addition, the first pixel rows A1 and the second pixel rows A2 arealternately arranged along the extending direction of the signal lines13. Therefore, in the scanning of the laser beam Lh in the reciprocatingmanner, it is sufficient that the laser beam Lh is moved to an adjacentpixel row at an end in the scanning direction v (−v) of the laser beamLh, and thus a moving distance can be minimized.

An irradiation width in a direction perpendicular to the scanningdirection v (−v) of the laser beam Lh is determined so as tosubstantially cover portions where the transistors Tr1 and Tr2 areformed. In this step, it is sufficient that only portions correspondingto positions where the thin-film transistors Tr1 and Tr2 arranged asdescribed with reference to FIG. 2 are formed are selectively irradiatedwith the laser beam Lh. That is, it is sufficient that only areasincluding upper portions of the gate electrodes (14 a) 14 b areselectively irradiated with the laser beam Lh.

After the irradiation of the laser beam Lh is performed as describedabove, as shown in FIG. 5D, the photothermal conversion layer 42 andbuffer layer 41 disposed on the semiconductor thin film 32A are removedby etching.

Next, as shown in FIG. 6A, an insulating stopper layer 33 ispattern-formed on a portion of the semiconductor thin film 32A to beformed into a channel region at a position where the stopper layer 33overlaps with the gate electrode (14 a) 14 b with the semiconductor thinfilm 32A therebetween.

Subsequently, as shown in FIG. 6B, an n-type semiconductor layer 34 madeof, for example, silicon containing an n-type impurity is deposited soas to cover the stopper layer 33.

Next, as shown in FIG. 6C, the n-type semiconductor layer 34 and thesemiconductor thin film 32A are patterned so as to have an island shapeabove the gate electrode (14 a) 14 b.

Subsequently, as shown in FIG. 6D, a metal film covering the n-typesemiconductor layer 34 is formed and then patterned, thereby forming asource electrode 22 s and a drain electrode 22 d both of which arecomposed of a second metal pattern 22. The source electrode 22 s and thedrain electrode 22 d are separately provided on the stopper layer 33.Furthermore, the n-type semiconductor layer 34 is also patterned so asto be separated on the stopper layer 33, thereby forming a source S anda drain D both of which are composed of the n-type semiconductor layer34. Accordingly, bottom-gate thin-film transistors Tr1 and Tr2 areobtained in which a channel region ch is constituted by themicrocrystalline semiconductor thin film 32A and the source electrode 22s and the drain electrode 22 d are connected to the source S and therain D, respectively, which are in contact with the channel region ch.Other wiring portions, for example, the scanning lines 11, the powerlines 12, the upper electrodes of the capacitive elements Cs, and partsof the signal lines 13, all of which are shown in FIG. 2 are formed atthe same time in the step of forming the source electrode 22 s and thedrain electrode 22 d.

As a result, as shown in FIG. 2, a thin-film transistor substrate (drivesubstrate) in which the scanning lines 11, the power lines 12, and thesignal lines 13 are arranged on each of the display areas 2 a of theglass substrate 1, and pixel-driving circuits including the thin-filmtransistors Tr1 and Tr2 and the capacitive element Cs are provided oneach of the sub-pixels a can be produced. By using the same process asthe process described above, other elements and wirings constitutingperipheral driving circuits (not shown) provided near the display areasare formed. As the peripheral driving circuit, for example, asignal-line-driving circuit is provided along the long-side direction xof the display area 2 and a scanning-line-driving circuit is providedalong the short-side direction y of the display area 2.

Next, a description will be made of a step of forming light-emittingelements on the thin-film transistor substrate prepared above. FIG. 7 isa view showing a cross-sectional structure of a pixel (sub-pixel) of anactive matrix organic EL display device and corresponds to the crosssection taken along line VII-VII in FIG. 2.

As shown in FIG. 7, a passivation film 51 is deposited so as to coverthe glass substrate 1 on which the circuit including the thin-filmtransistors Tr1 and Tr2 and the capacitive element Cs is formed, and aplanarizing insulating film 52 is formed on the passivation film 51. Acontact hole (not shown) reaching one of the source electrode 22 s andthe drain electrode 22 d (for example, the source electrode 22 s) of thedriving transistor Tr2 is formed in the passivation film 51 and theplanarizing insulating film 52. Next, a lower electrode 53 connected tothe source electrode 22 s via the contact hole is pattern-formed on theplanarizing insulating film 52. This lower electrode 53 is used as ananode (or a cathode) of an organic electroluminescent element EL andpattern-formed on each pixel. An auxiliary wiring 53 a having a shapeinsulated from the lower electrode 53 is formed at the same time in thestep of forming the lower electrode 53.

Next, an insulating pattern 54 is formed so as to widely expose acentral portion of the lower electrode 53 and to cover the periphery ofthe lower electrode 53. An opening portion of this insulating pattern 54becomes a pixel opening. This insulating pattern 54 also includes acontact hole reaching the auxiliary wiring 53 a.

Subsequently, a luminescent functional layer 55 made of an organicmaterial is formed so as to cover the lower electrode 53 exposed in theinsulating pattern 54. This luminescent functional layer 55 includes atleast an organic luminescent layer. The luminescent functional layer 55is formed by sequentially laminating, for example, from the anode side,a hole injection layer, a hole-transporting layer, the organicluminescent layer, and an electron-transporting layer, if necessary.

Next, an upper electrode 56 is formed so as to cover the luminescentfunctional layer 55. This upper electrode 56 is used as a cathode (or ananode) of the organic electroluminescent element EL and formed as acommon electrode for all pixels. This upper electrode 56 is connected tothe auxiliary wiring 53 a via a contact hole provided in the insulatingpattern 54.

Accordingly, the organic electroluminescent element EL in which theluminescent functional layer 55 including the organic luminescent layeris sandwiched between the lower electrode 53 and the upper electrode 56is formed on the planarizing insulating film 52. This organicelectroluminescent element EL is configured to be connected to thedriving transistor Tr2 in the lower electrode 53.

Next, a sealing substrate 57 is disposed so as to face a surface of theglass substrate 1, the surface having the organic electroluminescentelement EL thereon. The glass substrate 1 is bonded to the sealingsubstrate 57 with an adhesive sealant 58 therebetween. In the case whereareas for forming a plurality of display panels 2 are defined on thesingle glass substrate 1 as shown in FIG. 1, the glass substrate 1 andthe sealing substrate 57 are divided so that each of the display panels2 are separated from each other.

Subsequently, as shown in FIG. 8, flexible printed circuit boards 61,63, and 65 are connected to each of the divided portions by apredetermined procedure if necessary. These flexible printed circuitboards 61, 63, and 65 are, for example, substrates 61 for supplyingpicture signals, substrates 63 for supplying a power, and substrates 65for supplying scanning signals and power control signals, respectively.

A display device 59 is produced as described above.

In the display device 59 having the above structure, in each of thesub-pixels a, a picture signal written from the signal line 13 throughthe switching transistor Tr1 is held in the storage capacitor Cs. Acurrent corresponding to the amount of held signal is supplied from thedriving transistor Tr2 to the organic electroluminescent element EL. Theorganic electroluminescent element EL emits light with a luminancecorresponding to the value of this current.

According to the production method of the first embodiment, for example,as shown in FIG. 4 (see FIG. 2), in crystallization of the semiconductorthin film 32 by irradiation of the laser beam Lh, the laser beam Lh isscanned such that the scanning direction of the laser beam Lh is thesame with respect to the order of arrangement (i.e., layout) of thesource S and the drain D of the driving transistor Tr2. Thereby,portions of the semiconductor thin film 32 disposed above the gateelectrodes 14 b are constantly scanned by the laser beam Lh in adirection from the drain D side to the source S side (or in the reversedirection). Consequently, a difference in crystallinity between aportion of the semiconductor thin film 32 at the source S side and aportion of the semiconductor thin film 32 at the drain D side, theportions being disposed above the gate electrode 14 b, the differencebeing caused by a difference in the scanning direction of the laser beamLh, is constant in the driving transistors Tr2. Accordingly, the drivingtransistors Tr2 in which an on-current is uniform can be produced, thuspreventing uneven luminance of the organic electroluminescent elementsEL connected to the driving transistors Tr2.

In addition, the arrangement of the source S and the drain D of thedriving transistor Tr2 is reversed in adjacent pixel rows (the firstpixel rows A1 and the second pixel rows A2). Therefore, as describedabove, in order to scan the laser beam Lh so that the scanning directionof the laser beam Lh is the same with respect to the order ofarrangement (i.e., layout) of the source S and the drain D of thedriving transistor Tr2, scanning of the laser beam Lh is performed inthe arrangement direction of the sub-pixels a in a reciprocating manner.Consequently, the time necessary for the step of crystallizationannealing of the semiconductor thin film can be reduced.

Accordingly, a display device which has satisfactory display propertiesand in which uneven luminance of electroluminescent elements connectedto the driving transistors Tr2 is prevented can be produced within afurther reduced turn-around time (TAT).

Second Embodiment

FIG. 9 is a view showing an arrangement illustrating a second embodimentwhich is a modification of the first embodiment. The second embodimentto be described with reference to this figure differs from the firstembodiment in that a first pixel row A1 and a second pixel row A2 do notshare a power line 12, and a scanning line 11 and a power line 12 arearranged for each of the first pixel row A1 and the second pixel row A2.The arrangement of the thin-film transistors Tr1 and Tr2 provided ineach of sub-pixels a is the same as that of the first embodiment.

Specifically, the thin-film transistors Tr1 and Tr2 are arranged so thata channel length direction thereof is parallel to a short side of thesub-pixel a, that is, gate electrodes 14 a and 14 b extend in along-side direction of the sub-pixel a, i.e., in a short-side directiony of the display area 2 a.

Furthermore, in particular, when a row of sub-pixels a parallel to ascanning line 11 is defined as a pixel row, in each of the display areas2 a, first pixel rows A1 and second pixel rows A2 are arranged inaccordance with a source S/drain D arrangement of the driving transistorTr2. In the first pixel rows A1 and the second pixel rows A2, the sourceS and the drain D of the driving transistor Tr2 are reversely arrangedwith respect to the direction of the pixel rows. More specifically, ineach of sub-pixels a in the first pixel rows A1, the drain D and thesource S of the driving transistor Tr2 are arranged in that order in afirst direction (for example, in a direction from the left to the rightin FIG. 9). In contrast, in each of sub-pixels a in the second pixelrows A2, the drain D and the source S of the driving transistor Tr2 arearranged in that order in a second direction opposite to the firstdirection (for example, in a direction from the right to the left inFIG. 9).

Preferably, the first pixel rows A1 and the second pixel rows A2 arealternately arranged along the extending direction of the signal lines13.

A thin-film transistor substrate having the above arrangement isprepared by a procedure similar to that used in the first embodiment.

Specifically, as shown in FIG. 10, first, by the procedure describedwith reference to FIG. 5A in the first embodiment, gate electrodes 14 aand 14 b composed of a first metal pattern 21 are formed on each ofdisplay areas 2 a of a glass substrate 1, and furthermore, other wiringportions composed of the first metal pattern 21, for example, parts ofsignal lines 13 and lower electrodes of capacitive elements Cs, are alsoformed. In this step, the gate electrodes 14 a of switching transistorsTr1 and the gate electrodes 14 b of driving transistors Tr2 arepatterned so as to extend in a direction parallel to a short-sidedirection y of the display area 2 a. The parts of the signal lines 13are patterned so as to extend in the direction parallel to theshort-side direction y of the display area 2 a.

In particular, the gate electrodes 14 b of the driving transistors Tr2are provided such that a source S/drain D arrangement in an arrangementdirection of sub-pixels a is reversed every pixel row extending in adirection perpendicular to an extending direction of the signal lines13. More specifically, in each of the display areas 2 a, first pixelrows A1 and second pixel rows A2 are arranged in accordance with thesource S/drain D arrangement of the driving transistors Tr2. In thefirst pixel rows A1 and the second pixel rows A2, the source S/drain Darrangement of the driving transistors Tr2 is reversed in thearrangement direction of the sub-pixels a. The gate electrode 14 b ofthe driving transistor Tr2 is formed as a pattern that is continuouswith the lower electrode of the capacitive element Cs. A portionconstituting the gate electrode 14 b in this continuous pattern isprovided so as to extend in a direction parallel to the short-sidedirection y of the display area 2 a.

Next, a gate insulating film 31 made of, for example, silicon oxide orsilicon nitride is deposited so as to cover the first metal pattern 21,and a semiconductor thin film 32 made of amorphous silicon issubsequently deposited on the gate insulating film 31.

Subsequently, as shown in FIG. 5B, a buffer layer 41 made of siliconoxide or silicon nitride is deposited so as to cover the semiconductorthin film 32. Subsequently, a photothermal conversion layer 42 made ofmolybdenum (Mo) is deposited thereon.

Subsequently, as shown in FIG. 5C and FIG. 10, the semiconductor thinfilm 32 is indirectly irradiated with a laser beam Lh through thephotothermal conversion layer 42 and the buffer layer 41, thusperforming a heat treatment on the semiconductor thin film 32. In thisstep, a laser beam emitted from an oscillation source composed of asolid-state laser is irradiated as the laser beam Lh. Consequently, aportion of the semiconductor thin film 32, the portion being irradiatedwith the laser beam Lh, is formed into a microcrystalline silicon thinfilm 32A crystallized so as to have crystal grains on the nanometerorder.

In the irradiation of the laser beam Lh in this step, it is importantthat the semiconductor thin film 32 disposed above the gate electrode 14b be irradiated with the laser beam Lh while scanning the laser beam Lhsuch that the scanning direction of the laser beam Lh is the same withrespect to the arrangement of the source S and the drain D in adirection of a row of the sub-pixels a (i.e., here, in a directionperpendicular to the signal lines 13).

For this purpose, in this step, the scanning direction v (−v) of thelaser beam Lh with respect to the arrangement direction of thesub-pixels a is reversed between the first pixel rows A1 and the secondpixel rows A2. Specifically, for the first pixel rows A1, thesemiconductor thin film 32 is irradiated with the laser beam Lh in ascanning direction v (−v) of the laser beam Lh. In contrast, for thesecond pixel rows A2, the semiconductor thin film 32 is irradiated withthe laser beam Lh in a scanning direction −v (v) of the laser beam Lh.In particular, the scanning direction v (−v) of the laser beam Lh ispreferably determined so that the source S side of the drivingtransistor Tr2 is downstream and the drain D side thereof is upstream.Accordingly, the semiconductor thin film 32 is preferably irradiatedwith the laser beam Lh in the scanning direction v for the first pixelrows A1 and in the scanning direction −v for the second pixel rows A2.Consequently, each of the display area 2 a can be irradiated with thelaser beam Lh while scanning the laser beam Lh in a long-side directionx of the display area 2 a in a reciprocating manner.

In addition, the first pixel rows A1 and the second pixel rows A2 arealternately arranged along the extending direction of the signal lines13. Therefore, in the scanning of the laser beam Lh in the reciprocatingmanner, it is sufficient that the laser beam Lh is moved to an adjacentpixel row at an end in the scanning direction v (−v) of the laser beamLh, and thus a moving distance can be minimized.

An irradiation width in a direction perpendicular to the scanningdirection v (−v) of the laser beam Lh is determined so as tosubstantially cover portions where the transistors Tr1 and Tr2 areformed. In this step, it is sufficient that only portions correspondingto positions where the thin-film transistors Tr1 and Tr2 arranged asdescribed with reference to FIG. 9 are formed are selectively irradiatedwith the laser beam Lh. That is, it is sufficient that only areasincluding upper portions of the gate electrodes (14 a) 14 b areselectively irradiated with the laser beam Lh.

After the irradiation of the laser beam Lh is performed as describedabove, the same steps as those described in the first embodiment withreference to FIGS. 5D to 6D are performed. Thereby, the thin-filmtransistor substrate of the second embodiment shown in FIG. 9 can beproduced. Furthermore, in the case where electroluminescent elements areformed on this thin-film transistor substrate to produce an activematrix organic EL display device, the same steps as those described inthe first embodiment with reference to FIGS. 7 and 8 are performed.

According to the production method of the second embodiment, forexample, as shown in FIG. 10 (see FIG. 9), in crystallization of thesemiconductor thin film 32 by irradiation of the laser beam Lh, thelaser beam Lh is scanned such that the scanning direction of the laserbeam Lh is the same with respect to the order of arrangement (i.e.,layout) of the source S and the drain D of the driving transistor Tr2.Thereby, as in the first embodiment, portions of the semiconductor thinfilm 32 disposed above the gate electrodes 14 b are constantly scannedby the laser beam Lh in a direction from the drain D side to the sourceS side (or in the reverse direction). Consequently, the drivingtransistors Tr2 in which an on-current is uniform can be produced, thuspreventing uneven luminance of the organic electroluminescent elementsEL connected to the driving transistors Tr2. In addition, thearrangement of the source S and the drain D of the driving transistorTr2 is reversed in adjacent pixel rows (the first pixel rows A1 and thesecond pixel rows A2). Therefore, the time necessary for the step ofcrystallization annealing of the semiconductor thin film can be reduced.

Accordingly, also in the arrangement of the second embodiment, as in thefirst embodiment described above, a display device which hassatisfactory display properties and in which uneven luminance ofelectroluminescent elements connected to the driving transistors isprevented can be produced within a further reduced turn-around time(TAT).

Third Embodiment

FIG. 11 is a view showing an arrangement illustrating a third embodimentof the present invention. The third embodiment differs from the firstembodiment in that first pixel rows A1 and second pixel rows A2 arearranged in accordance with a source S/drain D arrangement of aswitching transistor Tr1. Other structures are the same as the firstembodiment.

In the first pixel rows A1 and the second pixel rows A2, the source Sand the drain D of the switching transistor Tr1 are reversely arrangedwith respect to the direction of the pixel rows. More specifically, ineach of sub-pixels a in the first pixel rows A1, the drain D and thesource S of the switching transistor Tr1 are arranged in that order in afirst direction (for example, in a direction from the left to the rightin FIG. 11). In contrast, in each of sub-pixels a in the second pixelrows A2, the drain D and the source S of the switching transistor Tr1are arranged in that order in a second direction opposite to the firstdirection (for example, in a direction from the right to the left inFIG. 11).

As in the first embodiment, preferably, the first pixel rows A1 and thesecond pixel rows A2 are alternately arranged so as to be adjacent toeach other along the extending direction of signal lines 13.

In the third embodiment, also regarding driving transistors Tr2, in thefirst pixel rows A1 and the second pixel rows A2, the source S and thedrain D of each driving transistor Tr2 are reversely arranged withrespect to the direction of the pixel rows. Here, in contrast to thefirst embodiment, in each of sub-pixels a in the first pixel rows A1,the source S and the drain D of the driving transistor Tr2 are arrangedin that order in a first direction (for example, in a direction from theleft to the right in FIG. 11). In contrast, in each of sub-pixels a inthe second pixel rows A2, the source S and the drain D of the drivingtransistor Tr2 are arranged in that order in a second direction oppositeto the first direction (for example, in a direction from the right tothe left in FIG. 11).

As in the first embodiment, the driving transistors Tr2 arranged in afirst pixel row A1 and the driving transistors Tr2 arranged in a secondpixel row A2, the first pixel row A1 and the second pixel row A2 beingalternately arranged, share a power line 12.

Other structure is the same as the first embodiment.

A thin-film transistor substrate having the above arrangement isprepared by a procedure similar to that used in the first embodiment.

Specifically, as shown in FIG. 12, first, by the procedure describedwith reference to FIG. 5A in the first embodiment, gate electrodes 14 aand 14 b composed of a first metal pattern 21 are formed on each ofdisplay areas 2 a of a glass substrate 1, and furthermore, other wiringportions composed of the first metal pattern 21, for example, parts ofsignal lines 13-1 (for first pixel rows A1), parts of signal lines 13-2(for second pixel rows A2), and lower electrodes of capacitive elementsCs, are also formed. In this step, the gate electrodes 14 a of switchingtransistors Tr1 and the gate electrodes 14 b of driving transistors Tr2are patterned so as to extend in a direction parallel to a short-sidedirection y of the display area 2 a. The parts of the signal lines 13-1and 13-2 are patterned so as to extend in the direction parallel to theshort-side direction y of the display area 2 a.

In particular, the gate electrodes 14 a of the switching transistors Tr1are provided such that a source S/drain D arrangement in an arrangementdirection of sub-pixels a is reversed every pixel row extending in adirection perpendicular to an extending direction of the signal lines13-1 and 13-2. More specifically, in each of the display areas 2 a,first pixel rows A1 and second pixel rows A2 are arranged in accordancewith the source S/drain D arrangement of the switching transistors Tr1.In the first pixel rows A1 and the second pixel rows A2, the sourceS/drain D arrangement of the switching transistors Tr1 is reversed inthe arrangement direction of the sub-pixels a.

The gate electrodes 14 b of the driving transistors Tr2 are alsoprovided such that a source S/drain D arrangement in an arrangementdirection of the sub-pixels a is reversed every pixel row extending in adirection perpendicular to the extending direction of the signal lines13-1 and 13-2. In this embodiment, in a single sub-pixel a, the sourceS/drain D arrangement of the switching transistor Tr1 is reverse to thesource S/drain D arrangement of the driving transistor Tr2. The gateelectrode 14 b of the driving transistor Tr2 is formed as a pattern thatis continuous with the lower electrode of the capacitive element Cs. Aportion constituting the gate electrode 14 b in this continuous patternis provided so as to extend in a direction parallel to the short-sidedirection y of the display area 2 a.

Next, a gate insulating film 31 made of, for example, silicon oxide orsilicon nitride is deposited so as to cover the first metal pattern 21,and a semiconductor thin film 32 made of amorphous silicon issubsequently deposited on the gate insulating film 31.

Subsequently, as shown in FIG. 5B, a buffer layer 41 made of siliconoxide or silicon nitride is deposited so as to cover the semiconductorthin film 32. Subsequently, a photothermal conversion layer 42 made ofmolybdenum (Mo) is deposited on the buffer layer 41.

Subsequently, as shown in FIG. 5C and FIG. 12, the semiconductor thinfilm 32 is indirectly irradiated with a laser beam Lh through thephotothermal conversion layer 42 and the buffer layer 41, thusperforming a heat treatment on the semiconductor thin film 32. In thisstep, a laser beam emitted from an oscillation source composed of asolid-state laser is irradiated as the laser beam Lh. Consequently, aportion of the semiconductor thin film 32, the portion being irradiatedwith the laser beam Lh, is formed into a microcrystalline silicon thinfilm 32A crystallized so as to have crystal grains on the nanometerorder.

In the irradiation of the laser beam Lh in this step, it is importantthat the semiconductor thin film 32 disposed above the gate electrode 14b be irradiated with the laser beam Lh while scanning the laser beam Lhsuch that the scanning direction of the laser beam Lh is the same withrespect to the arrangement of the source S and the drain D in adirection of a row of the sub-pixels a (i.e., here, in a directionperpendicular to the signal lines 13-1 and 13-2).

For this purpose, in this step, the scanning direction v (−v) of thelaser beam Lh with respect to the arrangement direction of thesub-pixels a is reversed between the first pixel rows A1 and the secondpixel rows A2. Specifically, for the first pixel rows A1, thesemiconductor thin film 32 is irradiated with the laser beam Lh in ascanning direction v (−v) of the laser beam Lh. In contrast, for thesecond pixel rows A2, the semiconductor thin film 32 is irradiated withthe laser beam Lh in a scanning direction −v (v) of the laser beam Lh.In particular, the scanning direction v (−v) of the laser beam Lh ispreferably determined so that the source S side of the switchingtransistor Tr1 is downstream and the drain D side thereof is upstream.Accordingly, the semiconductor thin film 32 is preferably irradiatedwith the laser beam Lh in the scanning direction v for the first pixelrows A1 and in the scanning direction −v for the second pixel rows A2.Consequently, each of the display area 2 a can be irradiated with thelaser beam Lh while scanning the laser beam Lh in a long-side directionx of the display area 2 a in a reciprocating manner.

In addition, the first pixel rows A1 and the second pixel rows A2 arealternately arranged in the extending direction of the signal lines 13-1and 13-2. Therefore, in the scanning of the laser beam Lh in thereciprocating manner, it is sufficient that the laser beam Lh is movedto an adjacent pixel row at an end in the scanning direction v (−v) ofthe laser beam Lh, and thus a moving distance can be minimized.

An irradiation width in a direction perpendicular to the scanningdirection v (−v) of the laser beam Lh is determined so as tosubstantially cover portions where the transistors Tr1 and Tr2 areformed. In this step, it is sufficient that only portions correspondingto positions where the thin-film transistors Tr1 and Tr2 arranged asdescribed with reference to FIG. 11 are formed are selectivelyirradiated with the laser beam Lh. That is, it is sufficient that onlyareas including upper portions of the gate electrodes (14 a) 14 b areselectively irradiated with the laser beam Lh.

After the irradiation of the laser beam Lh is performed as describedabove, the same steps as those described in the first embodiment withreference to FIGS. 5D to 6D are performed. Thereby, the thin-filmtransistor substrate of the third embodiment shown in FIG. 11 can beproduced. Furthermore, in the case where electroluminescent elements areformed on this thin-film transistor substrate to produce an activematrix organic EL display device, the same steps as those described inthe first embodiment with reference to FIGS. 7 and 8 are performed.

According to the production method of the third embodiment, for example,as shown in FIG. 12 (see FIG. 11), in crystallization of thesemiconductor thin film 32 by irradiation of the laser beam Lh, thelaser beam Lh is scanned such that the scanning direction of the laserbeam Lh is the same with respect to the order of arrangement (i.e.,layout) of the source S and the drain D of the driving transistor Tr2.Specifically, portions of the semiconductor thin film 32 disposed abovethe gate electrodes 14 b are constantly scanned by the laser beam Lh ina direction from the source S side to the drain D side. Consequently,the driving transistors Tr2 in which an on-current is uniform can beproduced, thus preventing uneven luminance of the organicelectroluminescent elements EL connected to the driving transistors Tr2.

FIG. 13 shows current characteristics of thin-film transistors preparedby changing the scanning direction of the laser beam during the abovecrystallization annealing. As shown in this graph, a drain current Idsobtained was significantly different between a thin-film transistorobtained when the source side was upstream of the scanning direction anda thin-film transistor obtained when the drain side was upstream of thescanning direction. However, in this third embodiment, a laser beam isscanned in the same direction with respect to the source S/drain Darrangement of the driving transistor Tr2 in all the sub-pixels a.Therefore, uneven luminance of the organic electroluminescent elementsEL connected to the driving transistors Tr2 can be prevented.

In particular, in the third embodiment, in crystallization of thesemiconductor thin film 32 by the irradiation of the laser beam Lh, thearrangement of the source S and the drain D of the switching transistorTr1 is also the same with respect to the scanning direction of the laserbeam Lh in all the sub-pixels a. Accordingly, switching transistors Tr1having uniform characteristics can be produced, and thus the organicelectroluminescent elements EL can be uniformly driven by theseswitching transistors Tr1.

FIG. 14 shows the relationship between a signal-writing time and acurrent value of thin-film transistors prepared by changing the scanningdirection of the laser beam during the crystallization annealing. Asshown in this graph, in a thin-film transistor obtained when the drainside was upstream of the scanning direction in the irradiation of thelaser beam, a large current value could be obtained within a shortsignal-writing time, as compared with a thin-film transistor obtainedwhen the source side was upstream of the scanning direction of the laserbeam. Accordingly, in the third embodiment wherein the drain side of theswitching transistor Tr1 is upstream of the scanning direction, theorganic electroluminescent elements EL can be uniformly driven within ashorter signal-writing time.

In addition, also in the third embodiment, the arrangement of the sourceS and the drain D of the thin-film transistors Tr1 and Tr2 is reversedin adjacent pixel rows (the first pixel rows A1 and the second pixelrows A2). Therefore, the time necessary for the step of crystallizationannealing of the semiconductor thin film can be reduced.

Accordingly, in the above-described arrangement of the third embodiment,a display device which has satisfactory display properties and in whichan on-off control of electroluminescent elements can be uniformlyperformed by the switching transistors Tr1 and the electroluminescentelements can be driven at a uniform luminance by the driving transistorsTr2 can be produced within a further reduced turn-around time (TAT).

In the third embodiment described above, in crystallization of thesemiconductor thin film 32, the switching transistors Tr1 are arrangedso that the drain D is disposed at the upstream side of the scanningdirection of the laser beam and the driving transistors Tr2 are arrangedso that the source S is disposed at the upstream side thereof.Alternatively, in addition to the switching transistors Tr1, the drivingtransistors Tr2 may also be arranged so that the drain D is disposed atthe upstream side. This arrangement is further preferable becauseelectroluminescent elements connected to the driving transistors Tr2 canbe driven with a larger current.

In the third embodiment, as in the second embodiment, a first pixel rowA1 and a second pixel row A2 may not share a power line 12, and ascanning line 11 and a power line 12 may be arranged for each of thefirst pixel row A1 and the second pixel row A2. In this case, thearrangement of the thin-film transistors Tr1 and Tr2 disposed in each ofthe sub-pixels a may be the same as the third embodiment. This structurecan also achieve the same advantage as in the third embodiment.

Fourth Embodiment

An arrangement of a thin-film transistor substrate for carrying out aproduction method of a fourth embodiment will now be describe withreference to FIG. 15. The fourth embodiment to be described withreference to this figure differs from the first embodiment and thesecond embodiment in an arrangement state of first pixel rows A1 andsecond pixel rows A2 described in the first embodiment and the secondembodiment. In the fourth embodiment, a display area 2 a is divided intotwo areas, i.e., a first area 2 a-1 and a second area 2 a-2 in along-side direction x. A feature of the fourth embodiment is that thefirst pixel rows A1 are arranged in the first area 2 a-1, and the secondpixel rows A2 are arranged in the second area 2 a-2. The structure ineach of the first pixel rows A1 and the structure in each of the secondpixel rows A2 may be the same as those in the first embodiment or thesecond embodiment.

That is, the arrangement state of sub-pixels a in the display area 2 aand the structure of the pixel circuit arranged in each of thesub-pixels a may be the same as those of the first embodiment and thesecond embodiment. In addition, similarly, when a row of sub-pixels aparallel to the long-side direction x of the display area 2 a is definedas a pixel row, in each of the display areas 2 a, the first pixel rowsA1 and the second pixel rows A2 are arranged in accordance with a sourceS/drain D arrangement of a driving transistor Tr2 or a switchingtransistor Tr1.

As in the first embodiment and the second embodiment, in the first pixelrows A1 and the second pixel rows A2, for example, as shown in FIG. 2 orFIG. 9, the source S and the drain D of the driving transistor Tr2 arereversely arranged with respect to the direction of the pixel rows(direction parallel to the long-side direction x of the display area 2a). More specifically, in each of sub-pixels a in the first pixel rowsA1, the drain D and the source S of the driving transistor Tr2 arearranged in that order in a first direction (for example, in a directionfrom the left to the right in FIG. 15). In contrast, in each ofsub-pixels a in the second pixel rows A2, the drain D and the source Sof the driving transistor Tr2 are arranged in that order in a seconddirection opposite to the first direction (for example, in a directionfrom the right to the left in FIG. 15).

In particular, according to the feature of the fourth embodiment, suchfirst pixel rows A1 and second pixel rows A2 are separately arranged inthe first area 2 a-1 and the second area 2 a-2, respectively, which areformed by dividing the display area 2 a into two areas in the long-sidedirection x.

A thin-film transistor substrate having the above arrangement can alsobe prepared by a procedure similar to that used in the first embodimentand the second embodiment.

In particular, when a semiconductor thin film deposited so as to cover agate electrode is irradiated with a laser beam to performmicrocrystallization, as shown in FIG. 15, the first area 2 a-1 on whichthe first pixel rows A1 are arranged can be irradiated with a laser beamin a scanning direction v while the second area 2 a-2 on which thesecond pixel rows A2 are arranged is irradiated with a laser beam in ascanning direction −v.

Also in the production method of the fourth embodiment, as in the firstembodiment and the second embodiment, in crystallization of thesemiconductor thin film by irradiation of a laser beam Lh, the laserbeam Lh is scanned such that the scanning direction of the laser beam Lhis the same with respect to the order of arrangement (i.e., layout) ofthe source S and the drain D of the driving transistor Tr2. Thereby, asin the first embodiment and the second embodiment, portions of thesemiconductor thin film 32 disposed above the gate electrodes 14 b areconstantly scanned by the laser beam Lh in a direction from the drain Dside to the source S side (or in the reverse direction). Accordingly,the thin-film transistors Tr2 for driving in which an on-current isuniform can be produced, thus preventing uneven luminance of organicelectroluminescent elements EL connected to the driving transistors Tr2.In addition, the first area 2 a-1 on which the first pixel rows A1 arearranged and the second area 2 a-2 on which the second pixel rows A2 arearranged are irradiated with laser beams at the same time. Consequently,the time necessary for the step of crystallization annealing of thesemiconductor thin film can be reduced.

Accordingly, also in the arrangement of the fourth embodiment, as in thefirst embodiment and the second embodiment described above, a displaydevice which has satisfactory display properties and in which unevenluminance of electroluminescent elements connected to the thin-filmtransistors is prevented can be produced within a further reducedturn-around time (TAT).

This fourth embodiment can be combined with the third embodiment.Specifically, as in the third embodiment, the first pixel rows A1 andthe second pixel rows A2 may be arranged so that the source S and thedrain D of the switching transistor Tr1 are reversely arranged withrespect to the direction of pixel rows (direction parallel to thelong-side direction x of the display area 2 a), for example, as shown inFIG. 11. That is, in each of sub-pixels a in the first pixel rows A1,the drain D and the source S of the switching transistor Tr1 arearranged in that order in a first direction (for example, in a directionfrom the left to the right in FIG. 15). In contrast, in each ofsub-pixels a in the second pixel rows A2, the drain D and the source Sof the switching transistor Tr1 are arranged in that order in a seconddirection opposite to the first direction (for example, in a directionfrom the right to the left in FIG. 15).

This structure can also achieve the same advantage as in the thirdembodiment.

Fifth Embodiment

An arrangement of a thin-film transistor substrate for carrying out aproduction method of a fifth embodiment will now be describe withreference to FIG. 16. The same components as those in the first tofourth embodiments are assigned the same reference numerals and symbols,and a description of the common structure is omitted.

The fifth embodiment to be described with reference to this figurediffers from the first to third embodiments in that when a row ofsub-pixels a parallel to a scanning line 11 is defined as a pixel row,in a single pixel row, a source S/drain D arrangement in a bottom-gatedriving transistor Tr2 is reversed in a direction of the pixel row.Other structure is the same as the first to third embodiments.

Specifically, as in the first embodiment described with reference toFIG. 1, a display area 2 a is defined in each of two display panels 2arranged on a glass substrate 1. In each of the display areas 2 a,sub-pixels a each having a rectangular shape in plan view are arranged.The sub-pixels a are arranged such that a long side of each of thesub-pixels a is parallel to a short-side direction y of the display area2 a. Furthermore, these sub-pixels a constitute substantially squaredisplay pixels each composed of a set of three sub-pixels, namely, a red(R) sub-pixel a(R), a green (G) sub-pixel a(G), and a blue (B) sub-pixela(B), the three sub-pixels a being arranged in a direction of a shortside of each of the sub-pixels a.

In particular, in the fifth embodiment, among the set of the threesub-pixels a(R), a(G), and a(B) constituting a display pixel, one of thesub-pixels a is reversely arranged with respect to the pixel rowdirection. In this embodiment, for example, a sub-pixel including theelectroluminescent element having the lowest luminous efficiency isarranged so that the source S/drain D arrangement of the sub-pixel isreversed in the pixel row direction parallel to a scanning line 11. FIG.16 shows an example of the structure in which blue sub-pixels a(B) arereversely arranged.

Although not shown in the figure, in all the pixel rows parallel to thescanning lines 11, the blue sub-pixels a(B) are reversely arranged. Inaddition, a blue sub-pixel a(B) and an adjacent green sub-pixel a(G)share a power line 12 connected to drains of driving transistors Tr2.

Other structure is the same as the first embodiment. In particular, inthe pixel-driving circuit described with reference to FIG. 3, each ofthe electroluminescent elements EL provided in the sub-pixels a(R),a(G), and a(B) emits light with a luminance in accordance with a currentvalue of the driving transistor Tr2. Therefore, the driving transistorsTr2 provided in the sub-pixels a(R), a(G), and a(B) have channel widthsthat are different depending on the luminous efficiency of theelectroluminescent elements EL for each color connected to the drivingtransistors Tr2. Specifically, in a sub-pixel including anelectroluminescent element EL for a color with a low luminousefficiency, the channel width of the driving transistor Tr2 isdetermined to be large. In this embodiment, for example, the luminousefficiency of a blue electroluminescent element EL is the lowest and thechannel width of the driving transistor Tr2 in the blue sub-pixel a(B)is the largest. The channel width of the driving transistor Tr2 in thegreen sub-pixel a(G) is the second largest, and the channel width of thedriving transistor Tr2 in the red sub-pixel a(R) is the smallest.

A thin-film transistor substrate having the above-described arrangementis prepared by the following procedure.

First, as shown in FIG. 17, first, by the procedure described withreference to FIG. 5A in the first embodiment, gate electrodes 14 a and14 b composed of a first metal pattern 21 are formed on each of displayareas 2 a of a glass substrate 1, and furthermore, other wiring portionscomposed of the first metal pattern 21, for example, parts of signallines 13 and lower electrodes of capacitive elements Cs, are alsoformed. In this step, the gate electrodes 14 a of switching transistorsTr1 and the gate electrodes 14 b of driving transistors Tr2 arepatterned so as to extend in a direction parallel to a short-sidedirection y of the display area 2 a. The parts of the signal lines 13are patterned so as to extend in the direction parallel to theshort-side direction y of the display area 2 a.

In particular, the first metal pattern 21 is formed such that, among aset of three sub-pixels a(R), a(G), and a(B), the sub-pixel a(B) isreversely arranged with respect to the pixel row direction.

The first metal pattern 21 including the gate electrodes 14 a and 14 bis formed by, for example, depositing a molybdenum (Mo) film by asputtering method, and then pattern-etching the molybdenum (Mo) filmusing a resist pattern as a mask. The material of the first metalpattern 21 is not limited to molybdenum (Mo) as long as the material isa refractory metal that is not readily degraded in a subsequent heatingstep.

Next, a gate insulating film 31 made of, for example, silicon oxide orsilicon nitride is deposited so as to cover the first metal pattern 21,and a semiconductor thin film 32 made of amorphous silicon issubsequently deposited on the gate insulating film 31.

Subsequently, as shown in FIG. 5B, a buffer layer 41 made of siliconoxide or silicon nitride is deposited so as to cover the semiconductorthin film 32. Subsequently, a photothermal conversion layer 42 made ofmolybdenum (Mo) is deposited on the buffer layer 41. This photothermalconversion layer 42 is a layer for absorbing an energy beam such as alaser beam described below and converting light energy to heat energy.Accordingly, any material may be used as the photothermal conversionlayer 42 as long as the material satisfies the conditions that, forexample, the absorption rate of a laser beam (energy beam) used incrystallization annealing in the subsequent step is high, thermaldiffusion rates to the buffer layer 41 and the semiconductor thin film32 are low, and the material has a high melting point so as not to bereadily degraded by heat generated in the subsequent crystallization.Alternatively, for example, carbon (C) may be used.

Subsequently, as shown in FIG. 5C and FIG. 17, the semiconductor thinfilm 32 is indirectly irradiated with a laser beam Lh through thephotothermal conversion layer 42 and the buffer layer 41, thusperforming a heat treatment on the semiconductor thin film 32. In thisstep, a laser beam emitted from an oscillation source composed of asolid-state laser is irradiated as the laser beam Lh. Consequently, aportion of the semiconductor thin film 32, the portion being irradiatedwith the laser beam Lh, is formed into a microcrystalline silicon thinfilm 32A crystallized so as to have crystal grains on the nanometerorder.

In the irradiation of the laser beam Lh in this step, the semiconductorthin film 32 disposed above the gate electrode 14 b is irradiated withthe laser beam Lh while scanning the laser beam Lh such that one of therow directions of the sub-pixels a (i.e., directions along a scanningline 11 in this embodiment) is determined as a scanning direction v. Inthis step, for the driving transistors Tr2 of the blue sub-pixels a(B),it is preferable that the laser beam Lh be scanned in the scanningdirection v in which the drain D of the driving transistors Tr2 is theupstream side.

An irradiation width in a direction perpendicular to the scanningdirection v of the laser beam Lh is determined so as to substantiallycover portions where the transistors Tr1 and Tr2 are formed. In thisstep, it is sufficient that only portions corresponding to positionswhere the thin-film transistors Tr1 and Tr2 arranged as described withreference to FIG. 16 are formed are selectively irradiated with thelaser beam Lh. That is, it is sufficient that only areas including upperportions of the gate electrodes (14 a) 14 b are selectively irradiatedwith the laser beam Lh.

After the irradiation of the laser beam Lh is performed as describedabove, the same steps as those described in the first embodiment withreference to FIGS. 5D to 6D are performed. Thereby, the thin-filmtransistor substrate of the fifth embodiment shown in FIG. 16 can beproduced. Furthermore, in the case where electroluminescent elements areformed on this thin-film transistor substrate to produce an activematrix organic EL display device, the same steps as those described inthe first embodiment with reference to FIGS. 7 and 8 are performed.

According to the above-described production method of the fifthembodiment, among a set of three sub-pixels a(R), a(G), and a(B)constituting a display pixel, the sub-pixel a(B) is reversely arrangedwith respect to the pixel row direction, and the two sub-pixels a(G) anda(B) share a power line 12. Accordingly, the space in the sub-pixels acan be saved, and thus the distance between wirings can be increased.Consequently, the yield can be increased by an effect of preventingshort-circuit.

In addition, in crystallization of the semiconductor thin film 32 by theirradiation of a laser beam Lh, the semiconductor thin film 32 isirradiated with the laser beam Lh in the single scanning direction vparallel to the pixel row. Accordingly, the semiconductor thin film 32is constantly scanned by the laser beam Lh in a direction from the drainD side to the source S side (or in the reverse direction) for each ofthe sub-pixels a(R), a(G), and a(B). Therefore, thin-film transistorsTr1 and Tr2 in which an on-current is uniform in each of the sub-pixelsa(R), a(G), and a(B) can be obtained. As a result, a display devicewhich has satisfactory display properties and in which uneven luminanceof electroluminescent elements EL connected to pixel circuits includingthe thin-film transistors Tr1 and Tr2 is prevented in each of theluminescent colors can be produced.

In particular, in the fifth embodiment, among the three sub-pixels a(R),a(G), and a(B), a sub-pixel a including the electroluminescent elementEL having the lowest luminous efficiency (blue sub-pixel a(B) in thisembodiment) is selected as the sub-pixel a that is reversely arranged.In addition, in crystallization of the semiconductor thin film, portionsof the driving transistors Tr2 of the blue sub-pixels a(B) are scannedby the laser beam Lh in a scanning direction v in which the drain D isthe upstream side. Thereby, the driving transistors Tr2 for the bluesub-pixels a(B) can provide a large drain current compared with thedriving transistors Tr2 of the red sub-pixels a(R) and the greensub-pixels a(G). This is apparent from the description in the thirdembodiment with reference to FIG. 13.

Accordingly, a blue electroluminescent element EL with a low luminousefficiency provided in a blue sub-pixel a(B) can be driven with a largercurrent. In the blue sub-pixel a(B), the largest channel width isnecessary for the driving transistor Tr2 compared with sub-pixels forother colors. However, since the driving current of the blue sub-pixela(B) can be increased as described above, the channel width can bedecreased accordingly. Thereby, the area occupied by the drivingtransistor Tr2 of the blue sub-pixel a(B) can be decreased.

APPLICATION EXAMPLES

The display devices produced by the above-described methods according toembodiments of the present invention can be used as display devices ofvarious types of electronic devices shown in FIGS. 18 to 22, forexample, a digital camera, a notebook personal computer, a mobileterminal device such as a mobile phone, and a video camera. The displaydevices display picture signals input to the electronic devices orpicture signals generated in the electronic devices as an image or apicture. Examples of the electronic devices to which an embodiment ofthe present invention is applied will now be described.

FIG. 18 is a perspective view showing a television to which anembodiment of the present invention is applied. The television accordingto this application example includes a picture display screen portion101 composed of a front panel 102, a filter glass 103, and the like. Thetelevision is produced by using the display device according anembodiment of the present invention as the picture display screenportion 101.

FIGS. 19A and 19B show a digital camera to which an embodiment of thepresent invention is applied. FIG. 19A is a perspective view, viewedfrom the front side. FIG. 19B is a perspective view, viewed from thereverse side. The digital camera according to this application exampleincludes a light-emitting portion 111 for a flash, a display portion112, a menu switch 113, a shutter bottom 114, and the like. The digitalcamera is produced by using the display device according an embodimentof the present invention as the display portion 112.

FIG. 20 is a perspective view showing a notebook personal computer towhich an embodiment of the present invention is applied. The notebookpersonal computer according to this application example includes a body121, a keyboard 122 used for inputting characters and the like, adisplay portion 123 for displaying an image, and the like. The notebookpersonal computer is produced by using the display device according anembodiment of the present invention as the display portion 123.

FIG. 21 is a perspective view showing a video camera to which anembodiment of the present invention is applied. The video cameraaccording to this application example includes a body 131, a lens 132for capturing an image of an object, the lens 132 being provided on aside face directing to the front, a start/stop switch 133 used for imagecapturing, a display portion 134, and the like. The video camera isproduced by using the display device according an embodiment of thepresent invention as the display portion 134.

FIGS. 22A to 22G are views showing a mobile terminal device, e.g., amobile phone, to which an embodiment of the present invention isapplied. FIG. 22A is a front view showing a state in which the mobilephone is opened, and FIG. 22B is a side view of FIG. 22A. FIG. 22C is afront view showing a state in which the mobile phone is closed, FIG. 22Dis a left side view of FIG. 22C, FIG. 22E is a right side view of FIG.22C, FIG. 22F is a top view of FIG. 22C, and FIG. 22G is a bottom viewof FIG. 22C. The mobile phone according to this application exampleincludes an upper casing 141, a lower casing 142, a connecting portion(hinge portion in this example) 143, a display 144, a sub-display 145, apicture light 146, a camera 147, and the like. The mobile phone isproduced by using the display device according an embodiment of thepresent invention as the display 144 or the sub-display 145.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2008-323361 filedin the Japan Patent Office on Dec. 19, 2008 and Japanese Priority PatentApplication JP 2008-077400 filed in the Japan Patent Office on Mar. 25,2008, the entire contents of which are hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. A display device comprising:first pixel rows each including thin-film transistors each having asource and a drain arranged in a first direction; second pixel rows eachincluding thin-film transistors each having a source and a drainarranged in a second direction opposite to the first direction; and aplurality of light-emitting elements connected to the thin-filmtransistors.
 10. The display device according to claim 9, wherein thefirst pixel rows and the second pixel rows are alternately arranged. 11.The display device according to claim 9, wherein, among thin-filmtransistors provided in each of pixels, at least one of a thin-filmtransistor for switching connected to a scanning line and a signal lineprovided on a substrate and a thin-film transistor for driving in whicha source or a drain is connected to the light-emitting element isdisposed so that an arrangement of the source and the drain in a pixelrow direction is reversed every pixel row.
 12. A display devicecomprising: sub-pixels each including a light-emitting element connectedto a pixel circuit having a thin-film transistor; pixel rows in whichthe sub-pixels are arranged along an arrangement direction of a sourceand a drain of the thin-film transistor; and display pixels each ofwhich is composed of a set of three or more of the sub-pixels that areadjacently arranged in the arrangement direction and in which the orderof arrangement of the source and the drain is reversed only in thethin-film transistor of the pixel circuit connected to thelight-emitting element having the lowest luminous efficiency among thelight-emitting elements provided in the sub-pixels.
 13. The displaydevice according to claim 12, wherein the thin-film transistor has abottom-gate structure, and a channel region of the thin-film transistoris composed of a semiconductor thin film crystallized by beingirradiated with an energy beam while scanning the energy beam along thearrangement direction.
 14. The display device according to claim 13,wherein the channel region of the thin-film transistor of the pixelcircuit connected to the light-emitting element having the lowestluminous efficiency is scanned by the energy beam in a direction inwhich a drain side is upstream.
 15. The display device according toclaim 12, wherein the thin-film transistor constituting the pixelcircuit has a channel width that is different depending on a luminescentcolor of the light-emitting element connected to the pixel circuit. 16.(canceled)
 17. A thin-film transistor substrate comprising: first rowseach including thin-film transistors each having a source and a drainarranged in a first direction; and second rows each including thin-filmtransistors each having a source and a drain arranged in a seconddirection opposite to the first direction.
 18. The thin-film transistorsubstrate according to claim 17, wherein the first rows and the secondrows are alternately arranged.